This invention relates to a method of employing an extruded, open-cell alkenyl aromatic polymer foam in roofing systems.
Roofing systems typically comprise multiple layers of various materials configured to protect and optionally to insulate a roof deck or upper surface of a structure or building. The roofing system protects the deck and the interior of the structure from the weather, including wind, rain, and other precipitation.
The critical component of a roofing system is the membrane. The membrane is a sheet or mat of a solid, elastomeric substance which protects the deck from the aforementioned weather elements. Conventional membranes include those of EPDM (ethylene-propylenediene elastomer), modified bitumen, and plasticized polyvinylchloride. The membrane may be dark, medium, or light in color, but is usually dark.
When installing a new roofing system, the membrane is placed or laid on top of the roof deck. A protective layer may be typically inserted between the membrane and the deck. The protective layer may take the form of an insulative plastic foam or, more commonly, a non-foam material such as a wood or wood composite panel. Commercially-employed plastic foams include polystyrene bead foam, closed-cell extruded polystyrene foam, and closed-cell polyisocyanurate and polyurethane foams.
Optionally, a paving layer may be placed or laid on top of the membrane. The paving layer typically comprises materials such as gravel or stone ballast, shingles, brick, or concrete. The paving layer functions to physically protect the membrane from foot traffic and direct exposure to sunlight and the weather.
When replacement or recovery roofing systems are installed in existing structures or buildings, they are often installed over existing roofing systems. In a typical recovery system, a protective layer is applied or laid on top of the existing roofing system, usually an old membrane or an old paving layer; a new membrane is applied or laid on top of the protective layer; and, optionally, a new paving layer is applied on top of the new membrane. The protective layer protects the new membrane from the rough and uneven surfaces often encountered on the upper surfaces of existing roofing systems, provides mechanical support underneath the new membrane, and, in the case of plastic foams, provides additional-insulation.
A problem commonly encountered with roofing systems is rupture of the membrane due to distortion or deterioration of the protective layer underneath the membrane. The distortion and deterioration problems arise from the exposure of the protective layer to extreme heat from direct sunlight or moisture buildup due to weather exposure. The membrane, which is typically dark and elastomeric, absorbs significant heat from the sunlight, and further does not allow for timely escape of moisture trapped underneath it. When the insulating and/or protective layer becomes distorted or deteriorated, the membrane and the protective layer may separate to form void pockets, which leave the membrane with diminished mechanical support on its undersurface. The diminished support renders the membrane more subject to rupture.
The source of distortion and deterioration problems of the material in the protective layer varies according to the nature of the material. Some materials are susceptible to heat, some are susceptible to moisture, and some have inherently low mechanical strength.
Extruded, closed-cell polystyrene foams offer excellent mechanical strength and water resistance, but can become distorted at high service temperatures (greater than 165.degree. F.) due to their relatively low heat distortion temperature. Such high service temperatures are typically encountered under a dark membrane in direct sunlight.
Expanded polystyrene bead foams typically better maintain,their shape in a high temperature environment than extruded, closed-cell polystyrene foams because they typically have better bowing characteristics. Their bowing characteristics are better because the coalesced expanded bead structure allows for greater mechanical relaxation compared to the solid, cellular form of extruded, closed-cell foams. However, the coalesced expanded bead structure also results in lower mechanical strength and lower resistance to water transmission.
Closed-cell polyisocyanate foams have high heat distortion temperatures (250.degree. F.-275.degree. F.), but have poor moisture resistance. Moisture weakens the cellular structure of such foams, and renders them subject to physical deterioration over time. Moisture also diminishes the insulation value of the foam. They are also relatively friable, which affects their handling characteristics.
Closed-cell polyurethane foams, like closed-cell polyisocyanate foams, have high heat distortion temperatures and poor moisture resistance. They are also relatively friable, which affects their handling characteristics.
Wood panels and wood composite panels have high heat distortion temperatures, but have poor moisture resistance. Moisture weakens the wood, and renders it subject to physical deterioration over time. Further, the panels provide little insulation compared to foams.
It would be desirable to have a foam which could be deployed underneath a membrane in a roofing system. It would further be desirable if such foam had a heat distortion temperature of about 190.degree. F. or more. It would further be desirable if such foam had excellent moisture resistance and mechanical strength similar to that of extruded, closed-cell polystyrene foams.